STORM WATER SYSTEM MANAGES UNSEASONAL HEAVY DOWNPOUR

Late Monday afternoon Saskatoon experienced an unusual rain event for this time of May; between 15 and 20 mm of rain fell across the city between 5:00 and 5:30 p.m.  Peak intensities of 100 mm per hour were recorded which statistically makes the storm greater than a one-in-ten year event.

“In comparison, a similar amount fell early in the morning Monday but was spread over a longer period of time which is why there was no flooding then,” says Andrew Hildebrandt, Senior Storm Water Engineer.

Most of the issues from yesterday’s storm were related to surface flooding.  Newer neighbourhoods are designed so that the pipe, pond, and surface drainage systems can handle severe storms, but older neighbourhoods were not designed in this manner.

“We know there continues to be storm water problem areas in a handful of locations around Saskatoon, and the flooding in those instances is usually confined to the roadway,” Hildebrandt says. 

“We discovered some of the ponding was the result of debris covering catch basins and in most cases, as soon as Public Works crews cleared the blockages, the basins drained as the water made its way to storm retention ponds and to the river.

The high water volume caused some manhole covers to come off which is also an anticipated occurrence of the planned design.  This is why the City advises caution and – if possible – to avoid flooded streets as they could be hiding an open manhole.”

Sanitary Sewer System

The city’s storm sewer system handles rainwater drainage, while the sanitary sewer system handles domestic sewage.

Over the past number of years, the City has constructed a number of infrastructure projects in order to protect homes from flooding due to sanitary sewage backups. 

“The City’s focus has been on protecting private property from sanitary sewer flooding,” Hildebrandt says.

Super-pipes and new lift stations have been installed to reduce the risk of the sanitary sewer flooding. In prior years, heavy rain events allowed storm water to get into the sanitary system, causing back-ups and property damage.

No reports of sanitary sewage flooding have been reported due to yesterday’s storm.

Additional information

- Extra Public Works staff was called in to respond to reports of flooding.

- Crews responded to reported locations and replaced manhole covers that were displaced last night.

- The majority of the basins drained within a short period, as designed.  Crews inspected locations reported flooded, some catch basins were covered with debris which was cleared away. 

- Inspections continue today for locations that were not attended to last night. 

- Public Works received 73 calls for flooded catch basins or other drainage issues (The City has approximately 12,000 catch basins)

- Public Works received 37 reports of displaced manhole covers (The City has 8,800 storm sewer manholes).

- Compost Depots were closed due to weather around 5:00 p.m. last night.  Both locations have been open today.

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